1. Field of the Invention
This invention relates to a compression-molded plastic article having a multilayer structure which is conveniently embodied in container closures, container closure liners or containers, a method for production thereof, and to an apparatus conveniently used in the method of production.
2. Description of the Prior Art
It is well known to those skilled in the art that there has been a widespread practice to mold containers for drinks and foods, closures therefor and liners for closures or like articles from synthetic resins. In the early stage of this practice, such articles were molded by injection molding. The injection molding technique, however, was found to have difficulty in producting these articles at high speeds and low costs enough to achieve industrial and commercial success. From this viewpoint, it has recently been proposed, and come into commercial acceptance, to produce these articles by a compression molding technique (see, for example, Japanese Laid-Open Patent Publication No. 245517/1985).
Generally, synthetic resins having low gas-barrier property, such as olefinic resins, are selected as raw materials for these products to be molded by compression molding (or injection molding) in view of their excellent mechanical properties and hygienic property. When a container molded from such a material holds a carbonated beverage such as a carbonated soft drink or beer, carbon dioxide gas may leak through the container wall because of its low gas barrier property In the field of producing containers by first producing a preform by injection molding or extrusion molding and then stretch blow-molding the preform, it has been proposed to provide a preform of a laminated structure composed of a layer of a resin having low gas-barrier property such as an olefinic resin and a layer of a resin having high gas-barrier property such as an olefin/vinyl alcohol copolymer in an attempt to solve the aforesaid problem of gas leakage.
The present inventors previously produced a compression-molded article of a laminated structure in the following manner in an attempt to solve the above problem of gas-barrier property in the production of containers or the like by the compression-molding technique. Specifically, the present inventors produced such an article by extruding a heat-molten synthetic resin material having a laminated structure comprising a first synthetic resin having low gas-barrier property and a second synthetic resin having high gas-barrier property laminated to one surface of the first resin by using a known lamination-extrusion device having the type disclosed in Japanese Patent Publication No. 3837/1953, and then compression-molding the extruded synthetic resin material having the laminated structure to form a compression-molded article of a laminated structure composed of an inside resin layer of the first synthetic resin and an outside resin layer of the second synthetic resin.
It has been found however that this compression-molded article of a laminated structure easily undergoes delamination between the inside resin layer and the outside resin layer, and is not commercially acceptable.